Mass Effect 3 prompts players to make difficult, galaxy-altering decisions throughout the main story. From deciding the fate of the Rachni Queen to heralding a golden age for the Krogan, Mass Effect 3 poses a series of moral quandaries that confound the Paragon/Renegade binary. The controversial ending to the series was so divisive because no matter what choice Shepard made, the consequences were unequivocally dire.
Despite most decisions being complex and nuanced, one of the most popular decisions involved negotiating a peace between the Quarian and the Geth. A solid majority of players took great pains to ensure that peace was an option between two fan favorite companions, Tali and Legion. Though their peoples had been at war for hundreds of years, Tali and Legion found a way to coexist on the Normandy thanks to Shepard's deft diplomacy. The player base's partiality to securing a peace, the ethics underpinning the decision, and the narrative satisfaction of negotiating the truce make it the ideal route forward for the Mass Effect franchise.
The Background Behind the Geth War
The Geth were created by the Quarians as mechanical servants to provide cheap labor and military power. Creating machines to ease the lives of their creators isn't morally problematic in and of itself, but once the Geth developed sentience, players are left questioning the difference between machine labor and slavery. Given that players overwhelmingly chose Paragon over Renegade in their playthroughs, it's plain to see that most players would have a problem with forced labor of a sentient underclass.
Once the Quarians called for the total extermination of the now-self-aware Geth, the Geth began retaliating against their makers. This led to an all-out war between the Quarians and the Geth that eventually forced the Quarians off of their home planet, resulting in their spacefaring migrant lifestyle. The justifications behind this war are morally gray to say the least. Mass Effect 3's imminent Reaper threat forces Shepard to take action in resolving the conflict one way or another.
Brokering a Peace Between the Quarians and the Geth
Shepard's role in securing a peace between the Quarians and the Geth spans the events of Mass Effect 2 and Mass Effect 3. Though the conflict itself is laden with moral nuance, the individual decisions players need to make to ensure peace are generally popular ones. Acquitting Tali at her trial, resolving the conflict between Tali and Legion, and completing both companions' loyalty missions are all no-brainers to the majority of players in Mass Effect 2. While Mass Effect is a true RPG where players are afforded a range of options, the popularity of these decisions made the possibility of peace in Mass Effect 3 canon for most players.
There's actually surprisingly little that players need to accomplish in Mass Effect 3 to ensure peace. Completing Legion's Geth Fighter Squadrons mission is a prerequisite, but most players will want to complete this anyway to boost their War Assets. With this, a powerful contingent of Geth are officially fighting alongside the technologically-savvy Quarians in the war against the Reapers. From there, players need at least a 75% Paragon or Renegade score to resolve the Quarian-Geth conflict once and for all on the Priority: Rannoch story mission. At this point in the game most players have reached the minimum Paragon/Renegade score to secure a lasting peace.
The Difficulty with Canonizing Peace in Mass Effect 4
Given that the decisions leading up to peace are overwhelmingly positive among the player base, it should come as no surprise that peace was the most popular decision. The problem is, BioWare appears to have officially made the "Destroy Ending" canon in the upcoming Mass Effect game. This ending results in the complete destruction of all synthetic life in the galaxy, including the Geth.
While it's entirely possible that the Geth could have survived the Destroy Ending, their survival is almost beside the point when it comes to making the Quarian-Geth peace canon. In the end, the player base overwhelmingly chose to support Tali and Legion equally, and the requisite decisions for peace were widely popular. The Geth-Quarian peace could simply stand as a narratively satisfying conclusion to their morally nuanced conflict just before the Geth were wiped out entirely. Unfortunately, it'll be a while before players know for sure whether their peace will really last.
A New Mass Effect game is in development.